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Re: OLTC Questions



Original poster: "Stephen Conner by way of Terry Fritz <teslalist-at-qwest-dot-net>" <steve-at-scopeboy-dot-com>

OK guys, thanks for your many helpful answers.

I found a source for the IRG4PF50WD device that Terry used. They are 13 UK 
Pounds ($20) from Farnell Electronic Components. I'm amazed that they can 
be pulsed at 750 amps, since the datasheet pulse rating is only 204. 
Cranking the gate drive up to 25V probably helped. Terry's results have 
inspired me to try running a single device at 400 amps. I'll try and find 
the same/similar transzorb devices that he used too. I have a big pile of 
75V MOVs that I was going to string in series, but I feel that transzorbs 
might be better (less shunt capacitance/tighter clamping)

I took on board the comments about the secondary model I used in my 
schematic. I hadn't really thought about the L/C ratio when I drew it: I 
just wanted a load for testing the driver circuit. I'm hoping to get plenty 
more inductance by using a large diameter (6") coilform wound with about 
2000 turns of fine wire (0.125mm, not sure what AWG). It will end up very 
short and stubby, about 10-12" tall. The topload will be a couple of pie 
plates/metal bowls/whatever I can find, around 3.5"x10". I did a resonance 
analysis with FANTC and it suggests the system will resonate around 85 kHz. 
This is higher than planned but since the IGBT handles more current than I 
thought, I can still achieve my target 100W -at- 400bps.

I have no idea how the system will perform. Sure the "gap" losses will be 
less, but the secondary losses will be more, and from what I heard here, 
the 400bps operation might reduce streamer formation. My feeling is that 
overall it may be similar or slightly less than a 4/20 NST mini coil.

Steve C.